With the coming into force of the post-war San Francisco Peace Treaty in late April 1952, the sovereignty of Formosa was still considered to be undetermined.
Letter: Secretary of State Acheson to the US Mission in the United Nations
Date: June 2, 1952
Subject: Policy of the United States with respect to atomic energy and the regulation of armaments
(4) FYI US position is that sovereignty over Formosa not yet finally determined therefore seek to avoid issue of whether Formosa part of China for purposes of determining numerical ceilings.
[ source: Foreign relations of the United States, 1952-1954. National security affairs, Volume II, Part 2 (1952-1954), page 958 ]
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[English version] https://www.twdefense.info/trust3/frus-1952aq.htm
[Chinese version] https://www.twdefense.info/trust3/frusch-1952aq.htm
[Chinese version] https://www.twdefense.info/trust3/frusch-1952aq.htm